Lasers and optical amplifiers may be implemented e.g. by using light-amplifying double clad fibers. A double clad fiber may comprise a core consisting of e.g. silica glass doped with erbium (Er) or ytterbium (Yb). The double clad fiber comprises an inner cladding surrounding the core, and an outer cladding surrounding the inner cladding.
An optical signal propagating in the core may be amplified if population inversion is provided in the core. The population inversion may be established by coupling pump light into the inner cladding. The pump light propagating in the inner cladding partly escapes from the inner cladding into the core where the pump light may be absorbed by the dopant ions, thereby maintaining the population inversion.
Simultaneous coupling of the signal and pump light into the fiber and out of the doubly clad fiber is problematic due to the concentric structure of the doubly clad fiber.
U.S. Pat. No. 6,826,335 discloses an optical fiber arrangement comprising at least two fiber sections, wherein the sides of said fiber sections are in optical contact with each other so that at least one of the sections can be separated from the other sections by pulling.